The study has a randomized, double-blind, placebo-controlled, double dummy and eight-way cross-over design. Males with T2DM on a stable metformin monotherapy will be screened for participation in the study. Eligible subjects will be randomized to receive DXM 30 mg, DXM 60 mg, DXM 90 mg alone or in combination with sitagliptin 100 mg, sitagliptin 100 mg alone, or placebo (for DXM and sitagliptin) on in total eight treatment days. An OGTT will be started 1 hour after study drug administration and blood glucose will be measured over the next 4 hours. There will be a 3 to 14-day washout period between doses.